1. Field of the Invention
The present invention relates to a chuck for receiving a rotary/percussion tool such as a drill bit, chissel, or bore-crown cutter.
2. Description of the Prior Art
Generally, a chuck for receiving a shank of a rotary-percussion working tool, e.g., such as disclosed in German Publication DE 3941 646 A1, has a shank-receiving sleeve with an inner cylindrical guide surface and with radially inwardly extending entraining webs, and radially inwardly displaceable locking members engageable in locking grooves of the tool shank, limiting axial displacement of the tool. Because of a high surface pressure, which is necessary for transmitting a predetermined torque, the radially inwardly projecting entraining webs are subjected to high wear which substantially reduces the service life of the chuck. A reduced wear of chucks is very important for their reliability, in particular, for those used in power tools used in mining for working concrete, mortar, and abrasive earth materials.
German Publication DE 38 43 465 A1 discloses a chuck with two entraining webs located radially inwardly with respect to guide surfaces, and with four, located radially outwardly with respect to the guide surfaces, entraining grooves which are axially offset relative to the entraining webs. The entraining grooves have a central angle of 45°. The inwardly located entraining webs are subjected to a strong wear which substantially reduces the chuck service life. Moreover, with four symmetrically distributed entraining grooves, the remaining central angle of 45° between the grooves, does not provide a sufficient guide space for the radially displaceable locking bodies which, therefore, are displaceable axially, which leads to an increased length of the chuck.
German Publications DE 196 04 283 A1 discloses a chuck having two entraining webs arranged radially inwardly with respect to the guide surfaces, and three, located radially outwardly with respect to the guide surfaces, entraining grooves symmetrically distributed over a circumference. With small entraining grooves having a central angle of less than 30, a suitable shank with small entrainable wings of less than 30 should be used. Because of the over-proportional dependency of the circumferential flexural strength of the entrainable wings on the surface pressure, and the elastic/plastic deformation of which leads to transformation of a surface contact to a linear contact that causes a substantial wear, with so small entrainable wings, the surface pressure and thereby a torque, which is transmitted by the surface area of the chuck, are limited.
Accordingly, an object of the present invention is a chuck having a reduced length and capable of transmitting high torques, without being subjected to a substantial wear.